WO 00/14183 and U.S. Pat. No. 6,103,099 to ExxonMobil teach a process for producing an isoparaffinic lubricant base stock which comprises hydroisomerizing a waxy, paraffinic, Fischer-Tropsch synthesized hydrocarbon feed comprising 650-750° F.+hydrocarbons, said hydroisomerization conducted at a conversion level of said 650-750° F.+feed hydrocarbons sufficient to produce a 650-750° F.+hydroisomerate base stock which comprises said base stock which, when combined with at least one lubricant additive, will form a lubricant meeting desired specifications. Hydraulic oils are claimed, but nothing is taught regarding processes to make or compositions of hydraulic oils having especially good air release, low foaming, or good additive solubility.
U.S. Pat. No. 6,090,758 to ExxonMobil teaches a method for reducing foaming of lubricating oils which comprise a wax isomerate base stock made from Fischer-Tropsch wax, said method comprising adding to the oil an antifoamant or solvent solution thereof, consisting of a high molecular weight polydimethyl siloxane oil with specific viscosity and spreading coefficient. Nothing is taught regarding processes to make or compositions of hydraulic oils having air release times of less than 1.0 minutes at 50 degrees C.
Castrol Anvol SWX® FM ISO 46 hydraulic oil has an air release by ASTM D 3427 of less than 0.5 minutes at 50 degrees C., a viscosity index of 183, demulsibility by ASTM D 1401 of 25 minutes, and sequence II foam tendency by ASTM D 892 of 80 ml. It is made from a polyol ester lubricant base oil having high fire resistance, low tendency to form varnish, and good biodegradability. Polyol ester lubricant base oils are very expensive. Because they cost much more than conventional hydraulic oil, polyol ester-based fluids are used primarily in applications where fire resistance, environmental compatibility, or both justify the higher expense. Castrol Anvol SWX® FM is a registered trademark of Castrol Industrial Americas.
What is desired is a hydraulic oil with very low air release and improved foam tendencies, and a process to make it. Preferably the hydraulic oil will be made using a high quality base oil that is readily available and at prices competitive to conventional Group II and Group III base oils.